docs: def get_field_definition(field_definition):
      """ Normalizes a field definition into its component parts, even if some are missing. """
      if not isinstance(field_definition, (tuple, list)):
          field_definition = [field_definition]
      else:
          field_definition = list(field_definition)
  
      if len(field_definition) == 1:
          field = [None, field_definition, None]
      elif len(field_definition) == 2:
          field = field_definition + [None]
      elif len(field_definition) == 3:
          field = field_definition
      else:
          raise ValueError("Invalid field definition format.")
  
      if not isinstance(field[1], (tuple, list)):
          field[1] = (field[1],)
      field[1] = tuple(name for name in field[1] if name is not None)
  
      return FieldDefinitionTuple(*field)